A compact disk (CD) is a high-volume and long lived data-storage medium. One recordable compact disk (CD-R) contains a polycarbonate disk that is coated with a dye layer, a metallized reflective layer, and a protective layer. A CD-R will be understood to be a compact disk that can be written on, typically by a laser beam as contrasted with a CD-ROM which information is replicated by injection molding. Cyanine, phthalocyanine, and metallized azo dyes are commonly used dyes coated in a polymer binder in the dye layer. The metallized reflective layer typically consists of gold in CD-R, and aluminum in CD-ROM. In a CD writer, a laser beam illuminates the dye polymers through the polycarbonate substrate as the disk spins. The illumination is turned on and off at selective locations determined by the input digital information. The heating by the laser causes the dye layer to chemically change at these locations, forming readable marks in the dye polymer. The degraded dye polymers in the marked regions are less reflective than the unmarked regions. During the reading process, a low-power laser scans the dye polymer layer in a recorded disk. The laser light is reflected directly from the unmarked regions, but is scattered or diminished in the marked regions. A sensor monitors the transitions between the marked and unmarked regions from the intensity of the reflective light, and converts it into a digital data stream. Similar to the above process, a CD-ROM differentiates the intensity of the reflective light by pits and lands in the compact disks. These pits and lands are pre-recorded by pressing the compact disks, typically mass produced.
The CDs are often coated with a printable surface opposite to the surface from which the information is recorded and retrieved. On the printable surface, a label is printed which can be logos, trademarks, text, graphics, and bar codes, etc., which are related to the information stored on the CD. The label also protects the CD from physical damage. Because the CD spins at high speed in the writer and the player, the CD label needs to be precisely balanced to the center of the disk for smooth rotation.
Labeling of CD disks has routinely been accomplished through screen printing methods. While this method can provide a wide variety of label content, it tends to be cost ineffective for run lengths less than 300-400 disks because the fixed cost on unique materials and set-up are shared by all the disks in each run. The screen printing technique is well described in the textbook "Graphic Arts Manual", edited by Janet and Irving Field, Arno/Musarts Press, New York, N.Y., 1980, pp. 416 to 418. In screen printing a stencil of the image is prepared, placed in contact with the CD and then ink is spread by squeegee across the stencil surface. Where there are openings in the stencil the ink passes through to the surface of the CD, thus producing the image. Preparation of the stencil is an elaborate, time consuming and expensive process.
Recently, significant increases in use of CD-R disks as a data distribution vehicle have increased the need to provide customized CD label content to reflect the data content of the disk. For these applications, the screen label printing presents a dilemma as CD-R disks are designed to allow customized user information to be recorded in standardized CD formats.
Initially, the customized label information was "hand written" on the disk surface using felt tipped markers. While this method allowed users to individually identify disks, it tends to be labor intensive, prone to human error in transcription, and aesthetically limited.
Other attempts to provide a CD-R labeling solution have incorporated digitally printed adhesive labels. Label stock for this type of CD-R labeling is available from a number of sources. These allow pre-cut labels to be printed using desktop or commercial inkjet, thermal wax transfer, or printers. An example of such labels is the STOMP Company's (Irvine, Calif.) CD Stomper package of die-cut CD labels that can be printed on a page-size ink jet or laser electrophotographic printer. Following printing, the labels can be applied manually with or without the aid of an alignment tool or a specially designed machine. This method can be labor intensive. It is also prone to human error in label transfer. Damage to the CD-R can result if the label is removed. System performance problems can occur due to disk imbalance or label delamination in the CD writer or reader.
Within the past several years, methods for direct CD labeling have been growing in prominence. These methods utilize the versatility and ease of the setup associated with digital printing to provide customized label content directly on a disk surface. The most commonly used direct CD printers incorporate ink jet or thermal wax transfer technologies. Examples of such printers are the AFFEX Corporation's (2522 Chambers Road, Suite 110, Tustin, Calif.) Multi Media Color Ink Jet Printer, and the FARGO Corporation's (Eden Prairie, Minn.) Signature CD Color Printer. These printers can either stand alone or be integrated into a computerized disk writing system reducing problems associated with labor, human error, disk damage, and imbalance. Within this category of applications, U.S. Pat. No. 5,317,337 describes an apparatus and method for printing label information on a CD. Both inkjet and laser electrophotographic printing are described, but the laser electrophotographic printing is limited to printing ink onto an intermediate drum and then transferring the image to the CD label, that is, offset printing. U.S. Pat. No. 5,518,325 disclosed a method and a system for CD label printing. U.S. Pat. No. 4,967,286 disclosed a method for transforming images between coordinates for CD label printing.
In summary, prior screen printing CD-label printing techniques are not economic for printing label images on a small number of disks. The digital printing methods in the prior art do not address continuous-tone printing.